In X-ray photography which is conducted in a medical field, etc., a rotating-anode X-ray tube assembly is generally used. The X-ray photography is, for instance, Roentgen photography, CT photography, etc. The rotating-anode X-ray tube assembly includes a housing, and a rotating-anode X-ray tube which is stored in the housing and radiates X-rays. A lead plate, which shields X-rays, is stuck to the inner surface of the housing. An X-ray radiation window, which passes X-rays radiated from the X-ray tube, is provided on the outer wall of the housing. A coolant, such as an insulation oil, is sealed in a space between the housing and the rotating-anode X-ray tube.
The rotating-anode X-ray tube includes an anode target, a cathode, and an envelope which accommodates the anode target and the cathode and has its inside reduced in pressure. The anode target can rotate at high speed (e.g. 10000 rpm). The anode target includes a target layer (umbrella-shaped portion) formed of a tungsten alloy. The cathode is located with eccentricity from the rotational axis of the anode target and is opposed to the target layer.
A high voltage is applied between the cathode and the anode target. Thus, if the cathode emits electrons, the electrons are accelerated and converged, and collide upon the target layer. Thereby, the target layer radiates X-rays, and the X-rays are discharged from the X-ray transmission window to the outside of the housing.
For example, the shape of a light-load X-ray tube assembly is substantially rotation-symmetric with respect to the axis of the X-ray tube. The housing is cylindrical, and includes a projection portion having a side surface to which a high-voltage receptacle is attached, an X-ray radiation window, and side plates which close both opening end portions of the cylindrical housing.
In the meantime, in recent years, in an X-ray tube assembly for CT photography use, etc., a housing including a first divisional part and a second divisional part has begun to be used in accordance with an increase in complexity of the shape of the X-ray tube, an increase in weight of the X-ray tube, and an increase in rotational speed of a rotating frame on which the X-ray tube assembly is mounted. The coupling surface between the first divisional part and second divisional part is parallel to the axis of the X-ray tube.